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For subs use the content of the @_, specially for big data sent to the function:
Don't use:
sub { my ($var1,$var2) = @_ ; }
The best way is to use the @_[0] it self or the shift:
sub { my $var1 = shift ; my $var2 = shift ; }
* If you use @_[?] you can't modifie it! Use shift if you need to write to the var.

I was pretty sure that was wrong when I read it, so I whipped out Benchmark:

#!/usr/bin/perl -w use strict; use Benchmark qw(cmpthese); sub shifter { my $a=shift; my $b=shift; my $c=shift; my $d=shift; my $e=shift; my $f=shift; return $a*$b*$c*$d*$e*$f; } sub assigner { my ($a,$b,$c,$d,$e,$f)=@_; return $a*$b*$c*$d*$e*$f; } sub direct { return $_[0]*$_[1]*$_[2]*$_[3]*$_[4]*$_[5]; } cmpthese(-5, { 'shifter' => sub {shifter(1,2,3,4,5,6);}, 'assigner' => sub {assigner(1,2,3,4,5,6);}, 'direct' => sub {direct(1,2,3,4,5,6);}, } );
Results:
$ perl testSubs.pl Benchmark: running assigner, direct, shifter, each for at least 2 CPU +seconds... assigner: 0 wallclock secs ( 2.06 usr + 0.02 sys = 2.08 CPU) @ 384 +577.33/s (n=800690) direct: 3 wallclock secs ( 2.04 usr + 0.00 sys = 2.04 CPU) @ 629 +222.22/s (n=1285501) shifter: 2 wallclock secs ( 2.09 usr + 0.00 sys = 2.09 CPU) @ 294 +563.31/s (n=616521) Rate shifter assigner direct shifter 294563/s -- -23% -53% assigner 384577/s 31% -- -39% direct 629222/s 114% 64% --
That's with perl 5.6.1... Maybe 5.8.0 optimized shift? But you'd have to keep the old values around and have a "front" entry in the AV, and I don't remember seeing anything about that.
--
Mike

In reply to Re: Re: Optimizing existing Perl code (in practise) by RMGir
in thread Optimizing existing Perl code (in practise) by JaWi

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